Every excavator gets the knock eventually. The bucket clunks when the operator changes direction, the linkage wanders, and a new set of pins buys you about two weeks before the slop comes back. That’s usually the sign the pins were never the whole problem. The bore they ride in has worn oval, and line boring is how you fix it without scrapping the arm or the bucket.
We do this work at the machine, on jobsites and rental yards across Livermore, the Tri-Valley and the East Bay. The arm stays on. So does the bucket.
New pins won’t fix a worn bore
A pin joint has three parts that wear: the pin, the bushing, and the bore in the ear or boss that holds the bushing. Pins and bushings are the cheap, replaceable parts. The bore is part of the structure.
Once a bushing loosens or the grease stops getting where it should, the bore starts wearing too. It doesn’t wear evenly. Load pushes the pin in the same few directions all day, so the hole goes egg-shaped. Press a fresh bushing into an oval bore and it can’t seat properly. It spins, walks out, or wears through fast, and you’re back where you started.
Parts makers put the replacement point at about 1.5 to 2.0 mm of radial clearance between pin and bushing. GFM’s guide to loose excavator pins lays out the repair sequence once you’re past that point: pull the pin, weld up the bore, line bore it, and press in new bushings. Skip the middle two steps and you’ve bought pins. Not a repair.
What is line boring?
Line boring machines a worn bore back to a true, round, correctly sized hole while the machine stays assembled. A boring bar runs through both ears of the joint, gets aligned to the original centerline, and cuts the bore back to size. Because the bar passes through both sides at once, the two bores come out on the same line. That’s where the name comes from. It’s also the part that matters. Two perfectly round holes that don’t line up will still eat pins.
On most heavy equipment the job goes like this:
- Pull the pin and remove the old bushing.
- Measure how far the bore has worn and in which direction.
- Build the bore back up with weld (bore welding) so there’s fresh metal to cut.
- Set up the boring bar, align it through both ears, and machine the bore to size.
- Press in new bushings and fit the pin, which is the pin and sleeve machining half of the repair.
Done right, the joint goes back to original clearance. Not close to it. Back to it.
Signs the bores need line boring, not just new pins
Operators usually feel it before anyone measures it. Watch for these:
- A clunk or knock when the stick or bucket reverses direction.
- Bucket teeth that won’t hold a clean grade line because the bucket rocks side to side.
- Bushings that spin in the bore or start walking out.
- New pins that go loose again within weeks.
- Grease that squeezes straight out of the joint instead of staying in it.
- Shiny, polished wear on one side of the pin only.
If you’re seeing two or three of those on one joint, stop buying pins. Measure the play first. Past about 1.5 mm, pins alone are money spent twice. And if you find a crack running out from the ear while you’re in there, that’s a structural repair first. Our welding repair crew preps, welds and reinforces it before the bore gets machined, so the new bore sits in sound metal.
Doing it at the machine saves the trailer trip
Without portable line boring, fixing a worn joint means pulling the boom, stick or bucket and hauling it to a machine shop. That’s a day each way plus transport, before anyone cuts metal. It adds up fast. On a rental fleet the lost days often cost more than the repair itself.
Our two mobile rigs carry the line boring equipment along with the welders, gas and consumables, so the whole sequence happens where the machine sits. Nothing gets hauled. We’ve done this kind of fleet work for a national equipment rental fleet across Bay Area job sites, where every day a machine sits in the yard is a day it isn’t rented. The full list of what we do on excavators, loaders, dozers and skid steers is on our heavy equipment welding page.
There are exceptions. A small attachment that fits in a pickup often gets a better result on the bench at our Livermore shop, where it can be clamped and positioned properly. We cover how to make that call in mobile welding or the shop.
While the bucket’s apart, look at the wear surfaces
A bucket with worn pin bores has usually been working hard for a long time, so the cutting edge and side plates are rarely in great shape either. One trip beats two. We rebuild the worn edges and plates, then lay a wear-resistant alloy over them. Hard-facing an excavator bucket explains when that pays and when it doesn’t.
How much does line boring cost?
It depends on bore size, how much the bore has to be built up, how many joints need it, and how easy it is to get at the machine. We don’t quote a flat number without seeing the job. Anything else is a guess.
What we can tell you up front: we work to a 4-hour industrial minimum of $600. That covers a full crew and a properly equipped rig on your site. If you have several joints or several machines in one yard, doing them in one visit makes much better use of that minimum than calling us out one pin at a time. Batch the work.
Permits matter too. On-site welding and cutting usually falls under a hot work permit from the local fire department, and the lead times differ by city. We’ve written up the specifics for Livermore, Oakland and Hayward.
Get the joint looked at
Send us the machine make and model, which joint is loose, where it sits, and a photo if you can get one. That’s enough for us to show up with the right boring bar setup and the right filler. Guessing wastes a trip. We’re a C-60 licensed welding contractor, license #1132921 (you can check it with the CSLB), with AWS certified welding specialists and full insurance, and certificates are available before work starts.
Call (925) 518-6694. Or request a quote online. The shop is at 3555c First St, Livermore, CA 94551, and the rigs cover Oakland, Hayward, Fremont, Tracy and the rest of the East Bay service area.